There is a known method for sealing fuel elements, wherein the welding is carried out by melting the casing end together with the plug using the non-consumable electrode in the atmosphere of shielding gases (U.S. Pat. No. 3,045,108).
The disadvantage of the method is in that the arc is ignited by the contact between the electrode and the cylindrical projection of the plug, wherein tungsten inclusions get into the weld pool which can reduce the strength and, correspondingly, the quality of a welding joint.
The other known method of sealing fuel elements by fusion welding comprises welding the plug made of the same material as the fuel element casing to one end of the casing made of 1X18H10T (1Cr18Ni10Ti) stainless steel; fuel loading followed by welding the second plug to another end of the casing, thereby tightly sealing the fuel element containing the fuel (see the book: authors A. G. Samoylov, V. S. Volkov, M. I. Solonin “Fuel elements of nuclear reactors”, Moscow, Atomenergoizdat, 1996, analog). This method discloses all the essential technological operations which are required to seal fuel elements, wherein an oscillator is used to ignite an arc.
In recent years, in view of the higher standards for performance characteristics of fuel elements of fast-neutron reactors (such as the radiation dose, coolant corrosive-erosive effect and temperature), high-chromium ferrite-martensite steels of the following grades: EI-852, EP-823, EP-900 are used in manufacturing of fuel elements casings.
The closest analog is the method of sealing fuel elements with the casing made of high-chromium steel, which comprises welding the plug made of the same material as the fuel element casing to one end of the casing, fuel loading followed by welding the second plug to the other end of the casing to form the weld joint assembly, and finally tempering the weld joints to remove quenching structures therefrom (see the book “Development, production and operation of fuel elements of power reactors” edited by Ph. G. Reshetnikov, vol. 2, Energatomizdat, 1995r, prototype).
The main disadvantage of such method of welding the steels of this grade is a tendency to form quenching structures and cold cracking after a certain period of time upon completion of the welding in these steels.
A drawback of the method is that an additional operation is required for producing high-quality weld joints for such steels, in particular, the weld joint tempering which is carried out at 740-760° C. for 20-30 min, keeping the time between welding operations and the subsequent tempering as short as possible. This operation carried out after tempering the weld seam is costly and increases complexity of the technology of fuel element manufacturing, especially when tempering the weld joint which seals the fuel element loaded with fuel.